1. Field of the Invention
The present invention relates to the preparation of crystalline benzoyl peroxide, and more particularly to the preparation of benzoyl peroxide crystals of reduced size.
2. Description of the Prior Art
Benzoyl peroxide is a well known compound having a broad usage in topical pharmaceutical preparations and toiletries, with particular popularity as the active ingredient in many acne creams and lotions. One of the desired characteristics of such products including benzoyl peroxide, is that the product should have as smooth a texture as possible, to gain greater consumer satisfaction. As benzoyl peroxide is highly insoluble, and is generally held in suspension when included in these products, it has been a prior practice to reduce particle size of the benzoyl peroxide by grinding or the like to particles ranging in size below 20-25 microns. Grinding of benzoyl peroxide is performed, for example, during the preparation of an emulsion or gel product, wherein the benzoyl peroxide suspended in a suitable vehicle, such as water, is placed in a colloid mill and ground at a gap of, for example, 0.005 inches-0.003 inches. Similarly, the particle size of the suspension of benzoyl peroxide may be mechanically reduced by treatment with a roller mill. While these techniques will reduce fine crystals to an acceptable size range, they are incapable of reducing the size of larger crystals.
In addition to the esthetic factors mentioned above, the reduction in the particle size of the benzoyl peroxide increases the effective surface area and thereby maximizes its medicinal efficacy, so that smaller amounts of the material may be necessary to provide a given level of therapeutic effect. The reduction of benzoyl peroxide crystals by grinding or milling, however, is undesirable as it is energy consumptive and potentially dangerous, as the benzoyl peroxide is sensitive to heat friction and percussion, and may cause explosions to occur during grinding.
A need, therefore, exists for a safer, more effective and controllable, and less energy consumptive way for reducing the size of benzoyl peroxide crystals.